Initiation device desensitized by fluids



June 23, 1959 M. E. SWANSON 2,891,477

INITIATION DEVICE DESENSITIZED BY FLUIDS Filed July 2s, 1955 .1 Fig.2 I

. Fig. 3

' INVENTOR MERRILL EDWARD SWANSON ATTORNEY United Sttes Patent 2,891,477INITIATION DEVICE DESENSITIZED BY FLUIDS Merrill Edward Sw'anson,Pitman, NJ., assignor to E. L du Pont de Nemours and Company,Wilmington, Del., a corporation of Delaware Application July 26, 1955,Serial No. 524,511

13 Claims. (Cl. 102-28) The present invention relates to a novelinitiation device. More particularly, this invention relates to aninitiation device especially suitable for use in an oilwell perforatingassembly.

A means widely used for perforating oil well casings involves the use oflined shaped charges of a high velocity detonating explosive. Generally,a plurality of perforations in a selected area is desired, and thepractice followed is to position several perforators as a group andinitiate them at one time. For elfective penetration, the lined cavityof the perforator must be free of any substantially incompressiblematerial. Because the casings to' be perforated are frequently filledwith water or oil or mixtures of water and oil, means to prevent thecavity from becoming filled with the liquid must be provided. Theproduction of self-sufiicient individual units is feasible, and ispresently being done; however, the cost of the units is necessarilyhigh. An alternative expedient in widespread use is to position theplurality of perforating units in a liquid-tight carrier havingdestructible parts through which the penetrating jet is directed. Towithstand the tremendous pressures encountered within the wells, thecarrier must be sturdily built, and is, therefore, relatively expensive.However, inasmuch as the carrier can be reused many times if undamagedby the detonation of the perforating units, this arrangement is muchfavored.

Despite intensive precautions to make the carriers leakproof, anoccasional leaker is encountered. When this occurs, the carrier isinvariably deformed by the pressures produced by the detonation of theperforators because the relatively incompressible liquid does not permitthe rapid expansion of the products of detonation throughout theinterior of the carrier, the casing is improperly perforated, if at all,because the jet could not form, and, worst of all, the assembly may bejammed in the casing so that the assembly cannot be raised to thesurface by the attached lowering cable and must be removed by one ormore costly operations. Such operations do not otherwise improve thewell and are most undesirable. Altogether, the consequences of a leakercan be so serious that additional safeguards are sought by v but isunaffected by ordinary climatic conditions. Addi tional objectives willbecome apparent as my invention is more completely described.

I have found that the foregoing objects may be attained when I positiona receptor having a metal shell with one integrally closed end and animpact-sensitive explosive charge partially filling said closed end inaxial alignment to an electric detonator haivng a metal shell with anintegrally closed end so that the respective integrally closed ends faceeach other but are spaced apart a distance such that when the spacebetween them is unobstructed, detonation of the detonator will produceinitiation of the receptor, whereas, on the other hand, when the spaceis obstructed, as by a liquid, detonation of the detonator will notproduce initiation of the receptor. The detonator and receptor may bemaintained in the described relationship by any means which will notprevent the entrance of liquid into the space between the ends and whichis itself not an obstruction. Initiation of the receptor will produceinitiation of the detonating fuse to which the receptor is attached.

The initiation device constructed in accordance with the presentinvention will preferably be located in the bottom of the carrier of theperforators, so that even the partial filling of the carrier willinactivate the device and thereby prevent initiation of the perforatorunits. Thus, when the carrier is raised, the failure can instantly bedetected and, after the repairs or corrections have been made to preventfurther leakage, the initiation de-. vice can be replacedv and the unitreused directly.

In order to more fully describe the present invention, reference is madeto the accompanying drawings in which two specific embodiments areillustrated. The invention can be incorporated in many designs andvariations, and these drawings are illustrative only. 7

In the drawings, Figure 1 represents the device of the present inventionwherein the detonator and receptor are retained in the desiredrelationship by a pair of strips; Figure 2 represents a preferredembodiment wherein the detonator and receptor are surrounded by a rigidtube having perforations in the portion enclosing the space; and Figure3 represents an outside view of the device of Figure 2 connected to alength of detonating fuse.

Referring now to the figures in greater detail, 1 represents a metaldetonator shell having an integrally closed end 4. Within the shell 1and adjacent to the closed end 4 is a base charge 5 of a detonatingexplosive.

Adjacent to the base charge 5 is the ignition charge 6,

and imbedded in the ignition charge 6 is the bridge wire 7 whichconnects the leg wires 8, thus forming an electrical ignition means. Theleg wires 8 are positioned within the sealing plug 9 which is crimped inshell 1, and

indicated by means of the curved strips 3 which have;

been cold-soldered to the walls of the shells.

, In Figure 2, the arrangement is similar to that de -scribed withrespect to Figure 1, except that tubing 14 Patented June 23, 1959.

having perforations 15 has been used instead of the strips 3 to positionthe elements, and receptor shell 2 contains a booster charge 13 of adetonating explosive in addition to the impact-sensitive charge 11.

In Figure 3, a length of detonating fuse has been connected to thedevice of Figure 2, and crimped in position by peripheral crimps 17 Theoperation of the device of the present invention is as follows: When afiring current is applied to the leg wires 8, bridge wire 7 becomesincandescent, ignition charge 6 is initiated, and in turn initiates basecharge 5. The detonation of charge fragments the shell, and particles ofthe end 4 are directed toward thereceptor shell 2. In the absence of anyinterference, the particles strike shell 2 with suflicient force toinitiate impact-sensitive charge 11, which in turn, either directly orby means of booster charge 13, produces initiation of detonating fuse16. If a liquid essentially fills the space between the end 4 of thedetonator and the end of the receptor, and the distance is suflicient,the particles from shell end 4 will not have enough force to initiatethe charge 11, and propagation to the detonating fuse 16 will not occur.

The contour of the end 4 of the detonator shell 1 has an effect on thedirection of travel of the particles formed when base charge 5detonates. If the end is flat or rounded, a random dispersion of theparticle occurs and the quantity directed toward the receptor representsonly a small proportion of the shell end. When the end 4 has an inwardlydirected concavity, on the other hand, the detonation wave is apparentlyfocused along the axis of the detonator, and the quantity of particlesdirected toward the receptor is increased. The concavity need not be ofsuflicient depth and degree for the formation of a jet such as producedby conventional shaped charges, although the formation of a jet wouldnot be harmful. Therefore, the provision of an inward- 1y directedconcavity in the end of the detonator shell represents a preferredembodiment in the device of the present invention.

The maximum distance over which initiation of a receptor from adetonator will occur depends primarily upon the strength of thedetonator, i.e., upon the nature and quantity of the base charge.Initiation over an unobstructed space of several feet is obtainable.However, the use of such a long-length device is undesirable under mostcircumstances. Therefore, the minimum separation required for consistentinactivation by the presence of a fluid between a receptor and adetonator capable of consistently producing initiation over the sameseparation when unobstructed is the primary importance. I have foundthat when a separation of less than 0.5 inch is used, extremely preciseconstruction of the device and exacting manufacture of the detonator areessential, otherwise a device is produced which may not function in theabsence of a liquid or which may not fail in the presence of the liquid.When the separation is at least 0.5 inch, and preferably at least 0.75inch, devices which perform consistently can be produced by ordinarymanufacturing procedures. Ordinarily, the separation will not exceed 4inches because greater spacing is unnecessary and causes the device tobe unwieldy.

The means for holding the detonator and receptor in axial alignment andat the predetermined spacing must be rigid and penetrable by a liquid.The structures shown in Figures 1 and 2 are representative of suchmeans. Many others, such as tubular screening, wire rods, etc. would befeasible. The means must not obstruct the space between the two metalshell ends, particularly between their centers.

The following table illustrates fully the performance of devicesprepared in accordance with the present invention. In each case, theconstruction used was that illustrated in Figure 2. The receptorconsisted of 3 grains of lead azide as the impact-sensitive charge andgrains of RDX as a booster charge compacted at a pressure of about 7000pounds per square inch within an aluminum shell having an outsidediameter of 0.240 inch and a bottom wall thickness of 0.023 inch. Thedetonator shells had an outside diameter of 0.240 inch and a bottomthickness of 0.023 inch. The bottom was headed (inwardly directedconcavity) to form a cone having a 60 apex.

Table I Detonator Space Test Be- Water Perform- N o. tween in ance BasePrimer Ignition ends Space Charge 1 Charge 1 Charge 1 (in.)

I 3 gr. LS.-." 1 N0...-- 10 D 01'! do No 10 D 0F 3 d0 do Yes... 0D ICE4. do do 3 Yes..- 0D 5F 5 2gr. RDX 1%gr.L.A. 1 gr. L.S. 4 No 5D 0F 6 doo do 1 Yes..- 0D 11! 1 L.A.Lead azide.

1 L.S.-Double salt oflead nitrate and a bis basic lead salt of4,6-d1nitro ortho-cresol.

The usual base, priming and ignition compositions found in electricdetonators may be used. Typical base charge compositions include tetryl,trinitrotoluene, pentaerythritol tetranitrate, RDX (cyclonite), etc.Typical priming charge compositions include nitromannite,diazodinitrophenol, mercury fulminate, lead azide, etc. Typical ignitioncompositions include the complex salt of lead nitrate with a lead saltof a nitrophenol, mercury fulminate, lead styphnate, tetryl-leadstyphnate compositions, diazodinitrophenol nitromannite compositions,etc. Similarly, the usual impact-sensitive compositions and boostercompositions may be used in the receptor. Typical impact-sensitivecompositions include lead azide, mercury fulminate, lead styphnate, etc.The booster compositions include RDX, trinitrotoluene, pentaerythritoltetranitrate, etc. However, in view of the high temperatures encounteredin oil wells, I prefer to use only compositions stable above C.Accordingly, the preferred detonator will contain a base charge of leadazide or RDX, a priming charge of lead azide, and an ignition charge ofa complex salt of lead nitrate and a basic lead salt of a nitrophenol.The preferred receptor will contain an impact-sensitive charge of leadazide or lead styphnate and a booster charge of lead azide or RDX.

In the embodiment depicted in Figure 1, lead azide has been used as boththe base charge in the detonator and as the impact-sensitive charge inthe receptor. Under such circumstance, no priming charge is needed noris a booster charge because the lead azide is effective in itself. Inthe case of the receptor, however, I prefer to use a booster charge ofRDX in conjunction with the impactsensitive charge of lead azide inorder to reduce the quantity of explosive required to initiate thedetonating fuse.

The device of the present invention is not subject to ordinary climaticconditions and special handling precautions are not needed. Many obviousmodifications and variations will occur to those skilled in the art, andI intend, therefore, to be limited only by the following claims.

I claim:

1. An initiation device for detonating fuse comprising a receptor havinga tubular metal shell with one integrally closed end, the other end ofsaid shell being adapted to receive detonating fuse, and at least animpact-sensitive explosive charge partially filling said closed end; anelectric detonator having a tubular metal shell with one integrallyclosed end positioned in axial alignment. with said receptor and havinga base charge of a detonating explosive inside said integrally closedend, said shells and their integrally closed ends forming liquidimpervious containers, the said closed ends of each facing each other,an unobstructed space between said closed ends, and a liquid penetrablemeans rigidly holding said receptor and said detonator in said spacedrelationship, the distance between the said closed ends of the receptorand the detonator being at least /2 inch, whereby sufiicient liquid maypass through said liquid penetrable means into said unobstructed space,to prevent the propagation of detonation from said detonator to saidreceptor.

2. An initiation device as claimed in claim 1, wherein said receptorcontains a charge of a less sensitive detonating explosive in additionto the charge of an impactsensitive explosive.

3. An initiation device as claimed in claim 1, wherein the distancebetween the said closed ends of the receptor and the detonator isbetween /2 and 1 inch.

4. An initiation device for detonating fuse comprising a receptor havinga tubular metal shell with an integrally closed end and at least animpact-sensitive explosive charge partially filling said shell at saidclosed end, the other end of said shell being adapted to receivedetonating fuse, an electric detonator having a tubular metal shell withan integrally closed end which has an inwardlydirected concavity andcontaining a base charge of a detonating explosive inside saidintegrally closed end, said shells and their integrally closed endsforming liquid impervious containers, said detonator being in axialalign ment to said receptor, the said closed ends of each facing eachother, an unobstructed space between said closed ends, and a liquidpenetrable means rigidly holding said receptor and said detonator insaid spaced relationship, the distance between the said closed ends ofthe receptor and the detonator being at least /2 inch, wherebysufficient liquid may pass through said liquid penetrable means intosaid unobstructed space, to prevent the propagation of detonation fromsaid detonator to said receptor.

5. An initiation device as claimed in claim 4, wherein said means forholding said receptor and detonator in said spaced relationshipcomprises a plurality of strips.

6. An initiation device as claimed in claim 4, wherein said means forholding said receptor and detonator in said spaced relationshipcomprises a tubular connecting piece containing a plurality of openings.

7. An initiation device for detonating fuse comprising a receptor havinga tubular metal shell with one integrally closed end, animpact-sensitive charge within said shell adjacent to said end, and adetonating charge of a less sensitive charge adjacent to saidimpact-sensitive charge,

the other end of said shell being adapted to receive detonating fuse, anelectric detonator having a tubular metal shell with one integrallyclosed end, said end having an inwardly directed concavity, said shellsand their integrally closed ends forming liquid impervious containers, abase charge of a detonating explosive within said shell adjacent to saidclosed end, an ignition charge of an initiating explosive adjacent tosaid base charge, electrical initiating means in initiation relationshipto said igniton charge, and a plug sealing said shell, said receptor andsaid detonator being in axial alignment with the integrally closed endof one facing that of the other, an unobstructed space of at least V2inch in length between said receptor and said detonator; and a rigidtubular element surrounding both said receptor and said detonator, saidelement having a plurality of openings in that portion surrounding saidspace, whereby sufficient liquid may pass through said liquid penetrablemeans into said unobstructed space, to prevent the propagation ofdetonation from said detonator to said receptor.

8. A device as claimed in claim 7, wherein all of said explosive chargesare stable at temperatures up to at least C.

9. A device as claimed in claim 7, wherein the impactsensitive explosivecharge is lead azide.

10. A device as claimed in claim 7 wherein the ignition charge is leadazide.

11. A device as claimed in claim 7, wherein the detonating chargeadjacent to the impact-sensitive charge in the receptor shell is RDX.

12. A device as claimed in claim 7, wherein said tubular element is ofmetal.

13. A device as claimed in claim 7, wherein said tubular element is ofmetal and is crimped about the plugcontaining end of said detonator.

References Cited in the file of this patent UNITED STATES PATENTS2,400,103 Cobb May 14, 1946 2,423,837 Martin July 15, 1947 2,475,281Hanley July 5, 1949 2,739,535 Rolland et a1. Mar. 27, 1956 2,759,417ONeill Aug. 21, 1956 FOREIGN PATENTS 677,824 Great Britain Aug. 20, 1952

